FG5803 is obtained in a three-step synthesis: In the first step 4-(4-fluorophenyl)-4,4-ethylenedioxybutylchloride (A) reacts with piperazine (B) to give 1-[4-(4-fluorophenyl)-4,4-ethylenedioxybutyl]piperazine (I), which is reacted with cyclohexylisocyanate (C) to form 4-[4-(4-fluorophenyl)-4,4-ethylenedioxybutyl]-N-cyclohexyl-1-piperazinecarboxamide (II). The protecting group is removed by HCl in ethanol and the final product is isolated, 4-[4-(4-fluorophenyl)-4-oxobutyl]-N-cyclohexyl-1-piperazinecarboxamide hydrochloride (III).